Presentation on theme: "University College of Medical Science & GTB Hospital, Delhi"— Presentation transcript:
1 University College of Medical Science & GTB Hospital, Delhi Cardiac Rhythm and Anaesthesia: Basics of ECG Abnormal rhythms relevant to anaesthetic practice Antidysrhythmic agents Management of perioperative arrhythmias Abnormal rhythms relevant to anaesthetic practice Management of perioperative arrhythmias Antiarrhythmic agentsDr. B. UmaUniversity College of Medical Science & GTB Hospital, Delhi
3 Objectives What is an ECG ECG indications Review of the conduction systemECG recordingECG paperECG leads5. ECG interpretation
4 What is an ECG?The electrocardiogram (ECG) is a graphic recording of the electrical potentials generated by the heart. The signals are detected by means of metal electrodes attached to the extremities and chest wall and are then amplified and recorded by the electrocardiographIntroduced by William Einthoven in 1901
6 ECG Indications Monitoring Diagnosis In the perioperative setting, ECG serves 2 main functions – monitoring and diagnosisECG monitoring is mandatory and standard of care during all kinds of proceduresWith appropriate lead combinations, most arrhythmias and myocardial ischaemic events can be diagnosed.
7 ECG Indications… Preoperative period Risk Assessment Assess the baseline cardiac statusInformation regarding MI, conduction or rhythm abnormalitiesReveals findings related to life threatening metabolic disturbances or susceptibility to sudden cardiac death
8 ECG Indications… Intraoperative period Monitoring to detect changes in rate and rhythm or myocardial ischaemiaMonitoring of proper function of pacemakers or implantable cardiac defibrillators in patients undergoing surgery with these devices in placeIn intraop period, besides detecting changes in rate & rhythm or myocardial ischaemia, it also enables the anaesthesiologist to monitor the proper function ;l
9 ECG Indications… Postoperative period Monitoring Important in high risk patients when new ischemic or rhythm changes are suspectedA postoperative 12 lead ECG is often obtained in high risk .....
13 P wave caused by atrialdepolarizationRight atrial activation reflected byascending limb of P waveDuration= sLeft atrial activation reflected bydescending limb of P waveDuration= sHence, total duration= s(maximum duration=0.11s)Maximum normal amplitude=2.5mm
14 QRS complex is caused by the ventricular depolarization QRS duration secQRS amplitudeS amplitude in V1 + R amplitude in V6 < 3.5 millivolt (mV)R in V5 or V6 < 2 mV
15 The ST segment and T wave reflect ventricular repolarization ST segment duration= sT wave duration=0.16 sT wave should be at least ⅛th but less than ⅔rd of the amplitude of the corresponding R wave
16 ECG LeadsLeads are electrodes which measure the difference in electrical potential between either:1. Two different points on the body (bipolar leads)2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)
17 ECG Leads The standard ECG has 12 leads: 6 Frontal plane leads 6 Horizontal plane leadsFrontal plane leads - oriented in frontal or coronal plane of the body and consist of standard leads I, II, III and augmented limb leads AVR, AVL, AVF.Horizontal plane leads - oriented in transverse or horizontal plane of the body and are formed by precordial leads V1-V6.
25 3 Electrode ECG monitoring Electrodes placed on the torso to reduce artifacts from limb movementRA/LA electrodes placed in right and left infraclavicular fossaeLL leg electrode below the left rib cageMost common mode in OR and ICUGood enough to detect HR and VFInadequate for detecting complex arrhythmias and ST segment monitoring
27 Modified Chest leadsModified chest leads (MCL) are useful in detecting bundle branch blocks and premature beats.Lead MCL1 simulates chest lead V1 and views the ventricular septum.Lead MCL6 simulates chest lead V6 and views the lateral wall of the left ventricleCS 5 (RA electrode placed under the right clavicle and LA electrode placed in the V5 position) for detection of anterior myocardial wall ischaemiaCB5 (RA electrode over the center of the right scapula and LA electrode in the V5 position) for detection of ischaemia and supraventricular arrhythmias
29 The Right-Sided 12-Lead ECG The limb leads are placed as usual but the chest leads are a mirror image of the standard 12-lead chest placementClinical significance: Patients with an acute inferior MI should have right-sided ECGs to assess for possible right ventricular infarction
30 Invasive Electrocardiographic Monitoring Esophageal electrocardiogram:Much closer to atria. Hence better option when p waves recording is uncertainDetection of posterior wall ischaemiaEsophageal electrodes incorporated into esophageal stethoscopes and welded to conventional electrocardiographic wires
31 : Intracardiac electrocardiogram: Endotracheal electrocardiogram: Multipurpose pulmonary artery catheter with 3atrial and 2ventricular electrodes for intracavitary ECGRelatively insensitive to electrocauteryEndotracheal electrocardiogram:Endotracheal tube with 2 electrodes embeddedDiagnosis of atrial arrhythmias in pediatricsIntracoronary electrocardiogram:Coronary guide wire during angioplasty is usedGreater detection of acute ischaemia
33 Documentation: name of the patient and the date and time it was recorded. Calibration signal: The amplifier gain is normally adjusted so that a 1 millivolt signal through the ECG amplifier results in a vertical deflection of 10 mm (two large ECG squares). All voltage measurements on the ECG depend entirely on the accuracy of this calibration signal.
34 Determining the Heart Rate Rule of 1500Heart rate=1500/no. of small boxes between adjacent RR intervalsRule of 300Heart rate=300/no. of big boxes between adjacent QRS complexes6/3 second ruleNo. of RR intervals in 3sec multiplied by 20orNo. of RR intervals in 6sec multiplied by 10Check source of rules
36 What is the heart rate?Count number of large boxes between first and second R waves= /7.5 large boxes = rate 40
37 What is the heart rate?Count 30 large boxes, starting from the first R wave. There are 8 R-R intervals within 30 boxes. Multiply 8 x 10 = Rate 80
38 RhythmNormal: Each QRS preceded by a P wave with a regular PR and RR interval and a rate between 60 and 100 bpmIrregularRegularly IrregularIrregularly IrregularTell that arrhythmias will be discussed in details in the next part
39 The QRS AxisThe QRS axis represents the net overall direction of the heart’s electrical activityDirection of the axis determined on the basis of the hexaxial reference system
40 The QRS AxisBy near-consensus, the normal QRS axis is defined as ranging from -30° to +90°.-30° to -90° is referred to as a left axis deviation (LAD)+90° to +180° is referred to as a right axis deviation(RAD)Some books mention normal range upto +100
41 Movement of the electrical impulse towards the positive electrode will result in a positive deflection on the ECG.Movement of the electrical impulse towards the negative electrode will result in a negative deflection on the ECG.Movement of an electrical impulse perpendicular to a line between the positive and negative electrodes results in a biphasic deflection on the ECG.
42 Determining the Axis Predominantly Positive Predominantly Negative Equiphasic
43 The Equiphasic Approach 1. Determine which limb lead contains the most equiphasic QRS complex. The fact that the QRS complex in this lead is equally positive and negative indicates that the net electrical vector (i.e. overall QRS axis) is perpendicular to the axis of this particular lead.2. Examine the QRS complex in whichever lead lies 90° away from the lead identified in step 1. If the QRS complex in this second lead is predominantly positive, than the axis of this lead is approximately the same as the net QRS axis. If the QRS complex is predominantly negative, than the net QRS axis lies 180° from the axis of this lead.
44 Equiphasic Approach: Example 1 The Alan E. Lindsay ECG Learning Center ;Equiphasic in aVF Predominantly positive in I QRS axis ≈ 0°
45 Equiphasic Approach: Example 2 The Alan E. Lindsay ECG Learning Center ;Equiphasic in II Predominantly negative in aVL QRS axis ≈ +150°
46 Two lead approach Look for net QRS deflection in leads I and aVF If both +ve – Normal axisIf I +ve & aVF predominantly –ve – Left axis deviationIf I –ve & aVF +ve – Right axis deviation
47 Calculation of Axis – Third Approach Calculate the net QRS deflection in lead I and aVFE.g. in lead I, Q wave measures 3 small squares & R wave measures 6 small squares - net deflection is +3Similarly, net deflection in aVF is -5Cardiac vector is thus sum of individual vectors from leads I and aVF
48 P Wave Best evaluated in standard lead II and lead V1 In standard lead II P wave is pyramidal with a rounded apexIn lead V1 biphasic P wave with an initial positive and a terminal negative deflectionAxis within 40°to 60°
49 P Wave – Clinical Significance P Pulmonale-Tall peaked P wave-Amplitude in lead II >2.5 mm-Duration WNL-Expression of right atrial enlargementP Mitrale-Double peaked, notched orcamel humped P wave-Negative deflection in V1> 1mm-Duration of notch > 0.04s-Expression of left atrial enlargement
50 PR IntervalPR interval - between beginning of P wave and beginning of QRS complexDuration = 0.12 to 0.20 secReflects time taken for conduction of impulse from SA node to the ventricles through the AV nodeLong PR interval: first degree heart block, hyperkalemiaShort PR interval: WPW syndrome
56 Q wavesPathologic Q waves are a sign of previous myocardial infarction.The precise criteria for pathologic Q waves:Q-wave 0.04 s in durationDeeper than one fourth of thefollowing R wave in voltageQ wave is deep usually greaterthan 4mm in depth
57 ST Segment Represents greater part of ventricular repolarization Merges smoothly and imperceptibly with the proximal limb of T waveLeaves the baseline immediately after its origin; hence not isoelectricFlat, downsloping, depressed: coronary ischaemia, hypokalemia, digitalis toxicityElevation: MICheck normal variant
58 T Wave Represents the repolarization of the ventricles Last half represents relative refractory periodPositive deflection in most leadsNegative deflection in AVRBiphasic in V1T wave inversion: coronary ischaemiaTall tented T wave: hyperkalemiaFlat T wave: hypokalemiaHeavily notched: pericarditis
59 ST-T segment: Significance ST-T segment is the component of ECG most sensitive to acute myocardial ischaemiaTransmural ischaemia→ ST elevation accompanied by tall positive (hyperacute) T wavesSubendocardial ischaemia→ ST depressionMyocardial infarction→ pathologic Q waves
60 QT IntervalInterval from the beginning of the QRS complex to the end of T waveRepresents the total duration of ventricular electrical activityCorrected QT interval (Q-Tc)= QT/√R-RNormal values= 0.39±0.04 s.
62 U WaveSmall rounded deflection (< 1 mm) that occurs immediately after T wave and has same polarity as T waveBest seen in leads V2-V4?repolarization of papillary muscles or purkinje fibresProminent U wave: hypokalemia, drugs e.g. dofetilide, amiodarone, sotalol, quinidine, procainamide, disopyramideInverted U wave: Sign of ischaemia
63 J PointThe J point in the ECG is the point where the QRS complex joins the ST segment.It represents the approximate end of depolarization and the beginning of repolarization as determined by the surface ECG.There is an overlap of 10 milliseconds.
64 Some Practical Points Skin prepared by- Hair should be shavedSkin cleaned with spiritAbrade skin lightlyMuscle tremor presents as artifact. Electrode should be placed over bony prominence.Electrodes – pregelled, disposableBroken electrodes to be discarded
65 Artifacts Equipments interfering with ECG: 60 hz power lines Electrocautery (mc)Cardiopulmonary equipmentDefibrillatorsTransplanted heart(pseudoartifact)
71 Arrhythmias Abnormality of cardiac rate, rhythm or conduction Most frequent perioperative cardiac abnormalityBoth during cardiac and non cardiac surgeriesWith general and regional anaesthesia
72 Factors contributing to perioperative arrhythmias Patient relatedAnaesthesia relatedSurgery related
73 Patient related factors Pre existing cardiac disease – higher incidence, more fatalCNS stimulation – SAH → ST-T changesOld age – Post-op AF frequent due to degenerative changes in atrial anatomy
74 Anaesthesia related factors Endotracheal intubationGeneral anaestheticsHalothane (reentry, sensitization to catecholamines), enflurane, sevoflurane (severe bradycardia), desflurane (QTc prolongation)Drugs blocking reuptake of catecholamines- ketamineLocal anaestheticsInadvertent intravenous injection of large dose - cardiac arrestHigh thoracic levels of regional anaesthesia- bradyarrhythmiasAbnormal arterial blood gas and electrolyte levelsHypercarbia, hypoxia, hypocarbia a/w hypokalemia
75 Surgery related factors Autonomic reflexesPeritoneal traction, pressure on vagus - sinus bradycardia, AV block, asystoleOculocardiac reflex- bradycardia, asystoleIJV cannulationCardiac surgeryRelease of aortic cross clampPlacement of venous cannulaeRetraction of the heartSuturing over the atrium